PM8002 or Placebo Plus Nab-Paclitaxel as First-line Treatment in Inoperable Locally Advanced/Metastatic TNBC

Inclusion Criteria: * Ability to understand and willing to provide written informed consent and to comply with scheduled visits and study procedures; * Female, aged 18 to 70 years (inclusive); * Histologically confirmed unresectable locally advanced or metastatic breast cancer with negative status for ER, PR, and HER-2. Testing results for all three markers conducted within 24 months prior to the initiation of the study by a local facility accredited by clinical research center are acceptable. If deemed necessary by the investigator during screening, subjects may provide additional biopsy to confirm the latest pathological; * Subjects who have not received prior systemic treatment（except endocrine therapy） for advanced breast cancer are eligible for the study. Subjects who have received Taxane-based chemotherapy during the neoadjuvant and/or adjuvant treatment phase are eligible, as long as the occurrence of relapse or metastasis is at least 12 months after the end of treatment; * Performance status as assessed by the Eastern Cooperative Oncology Group (ECOG) is 0-1; * Life expectancy of 12 weeks or more; * According to RECIST 1.1, the subject has at least 1 measurable lesion as the targeted lesion (the only bone metastasis or the only central nervous system metastasis should not be considered as a measurable lesion. A measurable lesion located at the previously irradiated radiation field or other local treatment area should not be selected as targeted lesion, unless the lesion shows unequivocal radiographic progression). Exclusion Criteria: * Previous treatment with immune checkpoint agonists (such as CD137 agonists) or immune checkpoint inhibitors (such as CTLA-4, PD-1, PD-L1, LAG3 monoclonal antibody, etc.) or anti-vascular endothelial growth factor (VEGF) target drugs; * Has uncontrolled or symptomatic brain or spine cord metastases; * Those who have had other active malignant tumors within 5 years prior to the study treatment, except for those that can be treated locally and have been cured ; * Poorly controlled hypertension (systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg); * With a history of hypertensive crisis or hypertensive encephalopathy; * With a history of abdominal fistula, tracheoesophageal fistula, gastrointestinal perforation, or intra-abdominal abscess within the last 6 months prior to the start of the study treatment; * Adverse events resulting from prior anti-tumor therapies should be assessed and graded according to the CTCAE 5.0 criteria, subjects whose AEs have not returned to Grade 1 or below; * Has uncontrollable pleural, pericardial, or abdominal effusions; * Has received allogeneic hematopoietic stem cell transplantation or organ transplantation.